People spend over $9 billion on Halloween every year, and a big chunk of that will be for Halloween costumes. Keeping us supplied with scary, funny, creative, sexy, and trendy costumes takes teams of designers busy all year long. But they swing into high gear when a new meme pops up just before Halloween.

3. THEY CAN DESIGN AND PRODUCE A COSTUME IN A MATTER OF DAYS.

A lot of costume interest comes from what’s been making headlines in the fall: Costumers have to be ready to meet that demand. “We’re pretty good at being able to react quickly,” says Pilar Quintana, vice-president of merchandising for Yandy.com. “Something happening in April may not be strong enough to stick around for Halloween.”

Because the mail-order site has in-house models and isn’t beholden to approval from big box vendors, Quintana can design and photograph a costume so it’s available within 72 hours. If it's more elaborate, it can take a little longer: Both Yandy and Weeks had costumes inspired by the Cecil the Lion story that broke in July 2015 (in which a trophy hunter from Minnesota killed an African lion) on their sites in a matter of weeks.

11. DEAD CELEBRITIES MEAN SALES.

It may be morbid, but it’s a reality: The high-profile passing of celebrities, especially close to Halloween, can trigger a surge in sales. “Before Robin Williams died, I couldn’t sell a Mork costume for a dollar,” Weeks says. “After he died, I couldn’t not sell it for less than $100.” This year, designers expect Hugh Hefner to fuel costume ideas—unless something else pops up suddenly to grab their attention. “Last year, when Prince died, that was almost trumped by [presidential debate audience member] Ken Bone,” Berman says. “He became almost more popular than Prince.”

Another thing about selling trendy costumes is that a customer won't want to wear the same costume a year later, so there's another sale coming. Read more secrets from Halloween costume makers at Mental Floss.